Chapter 5 Measurement of Atmospheric Pressure

the gasket with a pair of tweezers and immerse it into the beaker filled with filtered mercury toallow the mercury to adsorb the dirt. Then attach the gaskets during reassembly.(5) Filtering mercury and cleaning componentsFor the filtering the mercury, pour the mercury into the strain that stands on a beaker coveredby a thick paper (cross grained paper) (See Figure 5.17).First, filter mercury with a rough strain, then again with a fine strain. Repeat this twiceor more until no dust is found. Since this process requires a lot of time, this filtering workshould start as soon as the mercury is drained into the beaker.Wipe the glass cylinder with cleaning paper moistened with alcohol, being careful not torub off the marks. Scrape off excess dirt with a cutter, taking care not to damage the glasscylinder, then polish the surface with a toothbrush and toothpaste. Wipe the glass cylindersufficiently to remove moisture.Wipe the boxwood part (Figure 5.16, c) with the cleaning paper. Wipe the inside of thewash-leather bag (Figure 5.12, b) with the cleaning paper. Then, put single-filtered mercuryinto the bag up to about 1/3, hold the bag with one hand to prevent mercury from splashing,and rub it with another hand to allow the mercury to adsorb the dirt. Repeat this process untilthe dirt in the bag is not found.Filter the contaminated mercury again and repeat it until it becomes clean.Wipe dust off the ivory pointer with a brush and the paper softly. Take care not tomove or damage the ivory pointer, as it will affect index error. Wipe dust off the woodenframe and glass tube with a brush and the cleaning paper.Some barometers contain mica plates (Figure 5.2, 22) inside the brass cylinders (Figure5.2, 21). Remove the mica plates carefully and wipe dust off with the cleaning paper or abrush.Bubbles often cling to the inlet of the glass tube. Pull them out by inserting awell-dried iron wire (such as a needle).(6) Assembling the mercury cistern glass cylinderReassemble the glass cylinder in the reverse order of disassembly. Before reassembly, wipedust off with clean paper or brush very carefully.Hold the upper and lower parts of the glass tube, assemble it to the main body. Becareful not to mix up the upper and lower sides and its orientation or leave fingerprints.When the gasket comes off, soften and wash it well with mercury before setting it into thegroove.Place the boxwood (Figure 5.16) on the main body and cover it with the brass metal frame(Figure 5.16), paying careful attention to the marks and the gaskets.Attach the three screws (Figure 5.16) to the original positions. Tighten the screwswhile rotating the main body and adjusting the balance of screws to each other. Unbalancedtightening may result in mercury leakage or glass tube breakage.To clean the assembled mercury cistern (Figure 5.15), pour mercury through theclearance of the wooden base while filtering so that the mercury adsorbs dirt. To drain themercury, plug the opening of the tube (Figure 5.15, b) with a fingertip covered with afingerstall and turn the main body upside down. If this is done when the mercury is concave19